The present invention relates to a technique for duplicating data between storage systems without intervention of any host.
As a technique for avoiding data loss in a storage system due to disaster or the like, there is a remote copy for duplicating data in a storage system at a remote place. Here, assume that the storage system includes a storage control unit and a storage unit. In addition, the remote copy is a technique in which one storage system transfers data in its own storage system to another storage system at a remote place, and storing the data in a storage unit in the remote storage system. As for the remote copy, U.S. Pat. No. 6,408,370 discloses a technique for copying data between different storage control units without intervention of any host computer (hereinafter referred to as “host”).
In recent years, there is a demand for performing remote copy among three or more sites. Here the word “site” means a place where a host, a storage system and the like are installed.
As for remote copy among three sites, U.S. Pat. No. 6,209,002 discloses a technique in which data received from a first site is transferred in a lump to a third site by a second site. According to this technique, even if data in the second site is updated by the first site a plurality of times, finally updated data may be sent to the third site in data transmission. It is therefore possible to suppress the increase of the communication cost in transfer paths among the sites.